Communication devices such as mobile phones have expanded their functions including the connection to the Internet. To cope with increase in communication data, technologies such as, for example, Long Term Evolution (LTE)-Advanced have been developed. To support multiple bands and reduce device size, there has been suggested a multiplexer in which a duplexer and a filter are connected in parallel to an antenna terminal through a matching circuit as disclosed in, for example, Japanese Patent Application Publication No. 2013-62556.
In the LTE system, to cope with increase in communication data, new bands such as, for example, Band42 (3400 MHz to 3600 MHz) and Band43 (3600 MHz to 3800 MHz) have been added. However, the conventional LTE system is designed to support transmission and reception of signals with frequencies of, for example, 700 to 2700 MHz, and thus has difficulty in supporting transmission and reception of signals with high frequencies such as 3400 to 3800 MHz.